删除一个StringBuilder的最后一个字符

When you have to loop through a collection and make a string of each data separated by a delimiter, you always end up with an extra delimiter at the end, e.g.

for (String serverId : serverIds) {
    sb.append(serverId);
    sb.append(",");
}

Gives something like : serverId_1, serverId_2, serverId_3,

I would like to delete the last character in the StringBuilder (without converting it because I still need it after this loop).

Others have pointed out the deleteCharAt method, but here’s another alternative approach:

String prefix = "";
for (String serverId : serverIds) {
    sb.append(prefix);
    prefix = ",";
    sb.append(serverId);
}

Alternatively, use the Joiner class from Guava :)

As of Java 8, StringJoiner is part of the standard JRE.

Another simple solution is:

```plain text sb.setLength(sb.length() - 1);

A more complicated solution:

The above solution assumes that sb.length() > 0 … i.e. there is a “last character” to remove. If you can’t make that assumption, and/or you can’t deal with the exception that would ensue if the assumption is incorrect, then check the StringBuilder’s length first; e.g.

```java
// Readable version
if (sb.length() > 0) {
    sb.setLength(sb.length() - 1);
}

or

// Concise but harder-to-read version of the above
sb.setLength(Math.max(sb.length() - 1, 0));

sb.deleteCharAt(sb.length()-1)

In this case,

sb.setLength(sb.length() - 1);

is preferable as it just assign the last value to ‘\0’ whereas deleting last character does System.arraycopy

As of Java 8, there’s a new StringJoiner class built in.

StringJoiner sj = new StringJoiner(", ");
for (String serverId : serverIds) {
    sj.add(serverId);
}

2016年09月25日25分09秒

Another alternative

for (String serverId : serverIds) {
    sb.append(",");
    sb.append(serverId);
}
sb.deleteCharAt(0);

Alternatively,

StringBuilder result = new StringBuilder();
for (String string : collection) {
    result.append(string);
    result.append(",");
}
return result.substring(0, result.length() - 1);

StringBuilder sb = new StringBuilder();
sb.append("abcdef");
sb.deleteCharAt(sb.length() - 1);
assertEquals("abcde", sb.toString());  // true

Just get the position of the last character occurrence.

for (String serverId : serverIds) {
    sb.append(serverId);
    sb.append(",");
}
sb.deleteCharAt(sb.lastIndexOf(","));

Since lastIndexOf will perform a reverse search, and you know that it will find at the first try, performance won’t be an issue here.

Yet another alternative:

public String join(Collection<String> collection, String seperator) {
    if (collection.isEmpty()) return "";

    Iterator<String> iter = collection.iterator();
    StringBuilder sb = new StringBuilder(iter.next());

    while (iter.hasNext()) {
        sb.append(seperator);
        sb.append(iter.next());
    }
    return sb.toString();
}

I am doing something like this:

StringBuilder stringBuilder = new StringBuilder();
for (int i = 0;
i < value.length;
i++) {
    stringBuilder.append(values[i]);
    if (i < value.length - 1) {
        stringBuilder.append(", ");
    }
}

With Java-8 you can use static method of String class,

String#join(CharSequence delimiter,Iterable

public class Test {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>();
        names.add("James");
        names.add("Harry");
        names.add("Roy");
        System.out.println(String.join(",", names));
    }
}

OUTPUT

```plain text James,Harry,Roy

To avoid reinit(affect performance) of prefix use TextUtils.isEmpty:

```java
String prefix = "";
for (String item : list) {
    sb.append(prefix);
    if (TextUtils.isEmpty(prefix))
    prefix = ",";
    sb.append(item);
}

Yet another solution similar to the “prefix” solution above avoids multiple prefix assignments in the loop. i.e. Just in case the optimizer does not unroll the first loop iteration.

StringBuilder sb = new StringBuilder();
boolean firstEntry = true;

for (String serverId : serverIds) {
    if (firstEntry)
    firstEntry = false;
    else
    sb.append(",");
    sb.append(serverId);
}

You can use:

string finalString=sb.Remove(sb.Length - 1, 1).ToString();